Noise reduction circuit, power conversion device, and refrigeration apparatus

Abstract

A noise reduction circuit includes: noise canceler circuitry configured to inject a compensation current into a power line and ground to reduce a common mode noise current that flows through the power line and the ground into a commercial power supply from a power converter with a switching element connected to the commercial power supply; and overcurrent inhibitor circuitry provided on a compensation current path through which the compensation current flows, the overcurrent inhibitor circuitry being configured to inhibit application of an overcurrent to the noise canceler circuitry.

The invention claimed is: 
     
       1. A noise reduction circuit comprising:
 noise canceler circuitry configured to inject a compensation current into a power line and ground to reduce a common mode noise current that flows through the power line and the ground into a commercial power supply from a power converter with a switching element connected to the commercial power supply; and 
 overcurrent inhibitor circuitry provided on a compensation current path through which the compensation current flows, the overcurrent inhibitor circuitry being configured to inhibit application of an overcurrent to the noise canceler circuitry. 
 
     
     
       2. The noise reduction circuit according to  claim 1 , wherein the overcurrent inhibitor circuitry is connected in series on an electrical path of the compensation current path through which the compensation current flows. 
     
     
       3. The noise reduction circuit according to  claim 1 , wherein the overcurrent inhibitor circuitry is provided on a path through which the noise canceler circuitry injects the compensation current toward the power line between the commercial power supply and the power converter and toward the ground. 
     
     
       4. The noise reduction circuit according to  claim 3 , further comprising a DC power supply configured to supply power to the noise canceler circuitry, wherein
 the noise canceler circuitry comprises:
 a detection circuit configured to detect a common mode noise current flowing through the power line; 
 an amplifier configured to amplify a detection signal of the detection circuit using the DC power supply as a power source; and 
 an output capacitor for passing the compensation current from an output of the amplifier to the power line or the ground, wherein 
 
 the DC power supply forms a conductive path with one of the power line and the ground, 
 the output capacitor is connected between the other of the power line and the ground and the output of the amplifier, 
 the overcurrent inhibitor circuitry is switching circuitry configured to switch the compensation current path between conduction and cut-off or between high impedance and low impedance, and 
 the switching circuitry is connected between one of the power line and the ground and the DC power supply, or between the other of the power line and the ground and the output of the amplifier. 
 
     
     
       5. The noise reduction circuit according to  claim 4 , wherein the switching circuitry is configured to make the compensation current path conductive in response to a DC voltage being applied to the amplifier from the DC power supply, and to cut off the compensation current path absent application of a DC voltage to the amplifier from the DC power supply. 
     
     
       6. The noise reduction circuit according to  claim 5 , wherein the switching circuitry is configured to, when the compensation current path is in a conductive state, cut off the compensation current path in response to an absolute value of a neutral point voltage of the power line with respect to the ground fluctuating above a voltage that is √2×1.1 times a rated voltage in the commercial power supply, or in response to an overcurrent being applied to the amplifier. 
     
     
       7. The noise reduction circuit according to  claim 4 , wherein the switching circuitry is configured to place the compensation current path into a low impedance state in response to a DC voltage being applied to the amplifier from the DC power supply, and to place the compensation current path into a high impedance state absent application of a DC voltage to the amplifier from the DC power supply. 
     
     
       8. The noise reduction circuit according to  claim 7 , wherein the switching circuitry is configured to, when the compensation current path is in a low impedance state, place the compensation current path into a high impedance state in response to an absolute value of a neutral point voltage of the power line with respect to the ground fluctuating above a voltage that is √2×1.1 times a rated voltage in the commercial power supply, or in response to an overcurrent being applied to the amplifier. 
     
     
       9. The noise reduction circuit according to  claim 1 , wherein the overcurrent inhibitor circuitry is switching circuitry configured to switch the compensation current path between conduction and cut-off or between high impedance and low impedance. 
     
     
       10. The noise reduction circuit according to  claim 1 , wherein a voltage of a DC power supply configured to supply power to the noise canceler circuitry is a DC link voltage of the power converter. 
     
     
       11. The noise reduction circuit according to  claim 1 , wherein a voltage of a DC power supply configured to supply power to the noise canceler circuitry is lower than a peak value of a DC link voltage of the power converter. 
     
     
       12. The noise reduction circuit according to  claim 11 , wherein the DC power supply is connected to the power line via a coupling capacitor. 
     
     
       13. A power conversion device comprising:
 a noise filter connected between the commercial power supply and the power converter; and 
 the noise reduction circuit according to  claim 1 , the noise reduction circuit being connected closer to the commercial power supply with respect to the noise filter. 
 
     
     
       14. A refrigeration apparatus comprising the noise reduction circuit according to  claim 1 .